On the basis of the orthogonality between subcarriers, Orthogonal Frequency Division Multiplexing (OFDM) systems perform a symbol mapping operation, a subcarrier mapping operation and an IFFT/FFT operation to transmit signals.
A conventional OFDM system uses a 256, 1024 or 2048-point FFT/IFFT process, and a conventional FFT processor uses a pipeline scheme that connects radix-2 or radix-4 butterfly units, memories and multipliers in series to process data sequentially.
The pipeline scheme provides a high processing speed. However, the pipeline scheme has a limitation in that the total chip size increases because a memory, a multiplier and a Read Only Memory (ROM) must be provided at each stage.
Moreover, a recent 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) system uses a 24576-point FFT process for downlink Random Access CHannel (RACH) transmission and thus requires a very large amount of computation and a very large memory capacity. So the conventional FFT processor is impossible to use in the 3GPP LTE system.